Recent advances in the semiconductor processing industry and in x-ray crystallography for biochemical and medical applications have demonstrated the need for more intense, coherent beams of shorter wavelengths or higher brightness, than currently achievable with the newly developed far UV lasers and expensive synchrotron laser sources. Current femtosecond-regime laser-produced plasmas offer the potential of high brightness x-ray sources, but to date suffer from lower than needed photon fluxes due to large bandwidths and relatively large angular divergences in the x-ray beams produced. While there is currently work in progress to overcome these limitations (e.g., the recent patent application referenced above by this inventor), these efforts may be of more value as drivers for dense plasma recombination x-ray lasers than as direct producers of non-coherent x-rays. Other, earlier techniques are briefly described in the following paragraphs.
Free-electron lasers, for example, are candidates for UV and x-ray generation and are presently under development. However, these devices will require very high energy electron beams to reach these wavelengths. In addition to the high cost, technical complexity, and size of these electron beam sources, the gain of FEL devices will be small at these frequencies since the gain scales as 1/.gamma..sup.3, where .gamma./2 is the electron beam energy. It may not be possible to sustain laser oscillations if the gain is comparable to system losses. At present, no high power FEL's exist at sub-visible wavelengths.
Excimer lasers are another technology being developed for output in the UV regime. These devices are at present limited to significant gains in the region above about 2,000 Angstroms. They also require expensive and large electron beam systems for excitation, are limited to pulsed operation, and use highly toxic and corrosive gases.
Plasma lasers have recently been investigated and predictions of potential high energy operation have been made. At present, two techniques have been utilized to generate population inversions; high and low voltage plasma arcs and laser initiated plasmas. Both are limited in the volume of plasma produced and thus the present invention represents a significant improvement in the state-of-the-art of plasma lasers in several important aspects.